How a wet-wing fuel tank on a plane works

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I’ve read online on how airliners store their fuel in the wings of the plane, and especially how it’s not in a tank, but its just inside the wings.

How exactly does this work? Does this mean the wings have to be completely air tight? If the inside of the wings are mostly structural elements, how do they deliver the fuel while making sure that there aren’t areas in the wing structure where the fuel gets trapped?

In: Engineering

I’m not sure how it is on all planes, but on the ones I work on there are “bladders” inside the wings. The actual fuel would corrode the metal, and when airline manufacturers tried anti-corrosion coatings… it would come off and gunk up engines so bad they would completely stop running. So, they went to bladders inside the wings.

Again though, this is only on planes I’ve worked on.

I’m a UAS pilot/maintainer. I’ve only worked with wet wings on drones.

Wet wings have fuel cells, these are pretty much bags, inside of them. They are air tight and pressurized. The fuel cells are joined by a line that feeds to the rest of the fuel system.

I might try looking at the [Wikipedia page for this topic](https://en.m.wikipedia.org/wiki/Wet_wing), I think it answers your question fairly well.

First sentence of the article:
>A wet wing is an aerospace engineering technique where an aircraft’s wing structure is sealed and used as a fuel tank. Wet wings are also called integral fuel tanks.[1]

>A disadvantage of the wet wing is that every rivet, bolt, nut plate, hose and tube that penetrates the wing must be sealed to prevent fuel from leaking or seeping around these hardware components. This sealant must allow for expansion and contraction due to rapid temperature changes (such as when cold fuel is pumped into a warm wing tank) and must retain its sealing properties when submerged in fuel and when left dry for long periods of time. 

There’s also this [Quora thread](https://www.quora.com/How-do-the-wings-of-an-aircraft-store-fuel) that I found. The answer by Jayaprakash has a pretty cool picture of a tank-like object taking up almost the entire cross-section of the wing.

On airliners, the wing is a large hollow structure. This means that is can be sealed so that it can contain fuel. It is divided into a few large sections to create several tanks.
The top and bottom surfaces are a few millimeters thick – there is fuel on the inner surface.
The wing box isn’t fully air tight for two reasons: as the plane climbs and descends, the outside air pressure changes. A sealed container would explode if air wasn’t able to be rebalanced. The other reason is that fuel needs to enter (during refueling) and leave (as it’s burnt by the engines), so an equal amount of air needs to enter/leave to balance the pressures.
A series of pipes is fitted inside the box to allow air to flow in and out. These pipes go to a hole at the wing tip.

Yeah that would be ideal. One empty and one full would drastically alter the flight characteristics. I don’t know how bad.